Apparatus for preparing molding sand



May 21, 1929. I w, F|$HE 1,713,869

APPARATUS FOR PREPARING MOLDING SAND Filed Aug} 28, 1925 4 Sheets-Sheet 1 May 21, 1929.

w. FISHER APPARATUS FOR PREPARING MOLDING SAND V,

Filed Aug. 28, 1925 4 Sheets-Sheet.

Ma 21, 1929. w, FISHER 1,713,869

APPARATUS FOR PREPARING MOLDING SAND Filed Aug. 28, 1925 4 Sheets--Sheet May 21, 1929. w. FISHER 1,713,869

APPARATUS FOR PREPARING MOLDING SAND Filed Aug. 28, 1925 4 Sheets-Sheet 4 J02 J09 a5 Patented May 21, 1929.

UNITED STATES Parser orrics.

WAGER FISHER, OF BRYN MA'WR, PENNSYLVANIA.

APPARATUS FOR PREPARING Iv'IOLDING SAND.

Continuation of application filed April 6, 1922, Serial No. 550,151.

This application filed August 28, 1925.

Serial H0. 52,983.

A main purpose is to violently circulate a stream of water, which may contain various amounts of sand and binder, out of and back into a suitable compartment and while it is circulating, modify or adjust the binder or water until the binder solution (considered apart from the sand which it carries) attains a definite strength and then to deliver a controlled portion of this circulating stream to one or more jigging screens progressively of larger mesh in order to size the sand catching the sand and liquid that passes each screen in a separate tank and circulating the surplus back to the original stream.

The violent circulation secures homogeneity of binder solution and frees the sand grains from any adhering binder. I provide easily controlled means for diverting any desired portion of the stream through the sizing screens and settling tanks. This comprises a conduit, preferably a pipe, having branches with vertically adjustable outlets delivering respectively back to the compartment and to the sizing screens.

By changing the relative vertical adjustment of the outlets any desired portion of the whole stream is directed through either branch. An ordinary valve would here quickly choke with sand and be of little use.

Further purposes are to segregate the settling tanks from vibrating machinery in order to avoid the disadvantageous packing and disassociation of thebinder and sand incident to rapid vibration; to recirculate tailings from the sizing screens whenever they become unduly loaded with binder solution; to aidscreening above a settling tank by washing the screening mixture with liquid thrown from the settling tank.

Finrther purposes will appear in the specification and in the claims.

Figure 1 is a sectional elevation of simple apparatus for performing my I original process.

' Figure 2 shows in sectional elevation different apparatus for accomplishing the same result.

Figure 3 is a section upon line 3-3 of Figure 5 of still different apparatus for accomplishing the same result.

Figure 4 is a side elevation of Figure 3.

Figure 5 a top plan view of Figure 3.

Figure 6 shows in sectional elevation other apparatus that may be used.

Figure 7 is a perspective view illustrating a desirable form found well adapted to manufacture molding sand commercially.

Figure 8 is a side elevation of the apparatus shown in Figure 7, and illustrating additional features not seen in Figure 7.

Figure 9 is a top plan of Figurei8.

Figure 10 is a fragmentary elevation illustrating a modification.

Like numerals refer to like parts in all figures.

Describing in illustration and not in limitation and referring to the drawings Figures l6 are generally similar to Figures 1-6 in my Patent No. 1,551,788 of which this is a development and continuation.

In my former application referred to I disclosed and broadly claimed a process for preparing molding sand in which raw sand was agitated with water (usually in hinder solution) to disintegrate lumps and to loosen the grains of sand from adhering binder, then sized by screening while wet and loosened from binder and then passed into and permitted to settle in a binder solution of definite predetermined strength to give a molding sand of definite binder content.

I did not then realize the advantage of avoiding violent vibration in the settling tanks because of the disadvantageous ell'cct of such vibration upon settling, nor other advantageous features brought out in the specification and claims of the present application.

In Figure 1 I have shown a tank 10 filled. with water to some'line a a, above the bottom 11 of ascreen which is typified by the simple form shown. This screen is of general box form and is jigged vertically by shaft 15. These motions can synchronize or,

alternate giving any separate or combination jigging desired.

The jig box is shown as hung from links 16 to limit its ultimate movement.-

The raw molding sand is intended to-be fed into it through a chute 17. The finished product settles into the well 18 whence portions maybe periodically removed to a suitable container 19 by closing valve 20 and opening valve 21. i, y I

As thus shown inits simplest form, the iron oXide or other binder will be loosened from the sand grains by the ,agitation'with water to go intocolloidal solution, the sand screening like naked grains, all sand particles that pass the mesh of the screen settling with some rapidity to the bottom of the tank. On the way they become coated" somewhat with binder and as they settle at the bottom they trap more binder within their voids.

In Figure 2 a tank has a compartment 26 for receiving and agitating the raw sand witlrwater, and settling compartments 27 and 28. The tank 25 isv filled with water or with binder solution to some level b--?) above the tops of the partition walls 29 and 30. Raw sand is charged into the agitating chamber 26 from thechute 31. 32 is a centrifugal pump and agitator driven in any suitable way, discharging a stream of sand and water upon the screen 33which is 1 given continuous vertlcal and lateral pgging by suitable vertically and horizontally operatingrlinks and cranks such as links 34 and 34 connected to cranks 35, 35' upon rotating shafts 36, 36 and links .37 connected to cranks 38 upon shafts 39.

Y -Tho colloidal binder solution discharged upon the screen '33 drains through the screen falling back into the compartments 27 and28 of tank 25, flowing over the tops of the partition walls 30 and 29 back into the compartment 26 giving effective circulation of the solution. That part of the screen 33 which is directly above compartment 27 is of closer mesh than that directly above oompartment 28, and grains that fall into compartment 27 are thus all sizes not'too large to pass this closer mesh while grains that fall into compartment 28 are too large to pass, the smaller mesh but too small to be caught on the larger mesh. Everything too large to pass either mesh finally falls oil the edge of the screen into a-suitable container 40. I

the sand grains by' strong agitation in the presence of water in compartment 26; the

tlingcomp'artments 27 and 28 in any suitableway, as by shoveling it out periodically or removing it continuously bymeans of a suitable automatiescrew' or belt conveyor (not shown).

In Figures 3 to 5 the apparatus shown in; cludes a tank of special form, to be filled with water or with a colloidal solution of oxide of iron or clay or of other binder to some level 0 c. It is divided into communieating compartments. I showalso a hopper 41 for raw sand, a successionof screen-- ing chambers (only two in the apparatus shown) 42 and 43, sloping screens 44* and 45 (one screen in each chamber), settling wells 46 and 47 (one settling well beneath each screen) and a settling well 48 after the last screen.

settling well). The 'pulsator standpipe compartments 52 and53 (one for each screening chamber) are open to the screenin chambers beneath'the screensv at one end eac 1 and are open to the atmosphere at the top. The screening chambers are provided with a common lid 54, sealing these chambers from'the atmosphere and in it is supported a pressure pulsator diaphragm 55.

Raw sand charged into the hopper 41is continuously delivered through the adjustable gate'56 to the sloping screen 44 where it is screened by reason of the pulsation of water or solution through the mesh of screen 44; sandtoo coarse to pass the mesh of the firstscreen is delivered through theadjustable gate 57 to a second sloping screen 45 having a mesh more coarse than in screen 44. The pulsation of solution through the mesh of screen 45 results in proper screening and sizing, grains that will pass screen 45 doing'so and grains too large to pass screen 45 being'delivered through the adjustable gate 58 into the settling'well 48.

The sand settling into the wells 46, 47 and The sand is removed-through conveyor pipes 49, 50 and 51 (one for each 48 is removedby the screw conveyors 59, 60

and 61, being delivered into any suitable re: ceptacles 62, 63 and 64.

The screening chambers are in air communication at the, top and water communication at the adjustable gates. Air pressure above the solution in the screening chambers pulsates by reason ofthe pulsation given the diaphragm 55. This action creates pulsation through the screens 44 and 45; also a pulsation through the adjustable hopper gate 56 but has little effect in creating pulsation through the gate 57 or through the gate 58.

It is obvious that pulsation through the screens can be brought about otherwise than as shown, and that such variation in the way of creating pulsation at the screens does not in any way affect the broad principles involved.

In Figure 6 raw sand from a hopper is delivered at anydesired rate by means of a worm 66 to a rough jigging screen 67 to remove pebbles, from which it passes down into the agitating chamber 68 of the tank 69 which is filled with water to some level all (i. i

The sand and water in the chamber 68 are maintained in violent agitation by means of the centrifugal pump and agitator 7 0 which simultaneously agitates the raw sand to loosen the binder and delivers a continuous stream of sand and water and loosened binder to the jigging screen 71 which is of finer mesh than the screen 71. Sand particles that pass the screen 71 drop into the settling chamber 72 with water and loosened binder and the molding sand product may be continuously removed by means of a worm 7 3.

The agitation chamber 68 and the settling chamber 72 are separated from one another by a partition 73 approximately tight in its lower portion 74 and with an upper portion 75 that is merely a fine mesh screen. The water solution of binder in the two chambers 68 and 72 for this reason maintains nearly the same level, the water delivered by the pump upon the screen 71 and drains down into the chamber 72, flowing back through the screen into the chamber 70.

The screens 67 and 71 are hung by vertical links 76, 77 and 76, 77 respectively, and a revolving cam and shaft 78 in conjunction with springs 79' and 80 maintains these screens in continuous jigging.

A water pipe 81 with valve 82 is shown above the screen 67 for constantly adding the requisite amount of water.

I have diagrammatically illustrated a temperature control device at 83 which may be of any well known type to secure and maintain the intended temperature of solution where such control is desired.

The figures thus far describedare generally the same as in the first application.

The apparatus illustrated in Figures 710 has features of Figures 2 and 6, with additional features that I now find desirable.

In Figure 6 the raw sand is delivered into the disintegrating and digesting tank 68 through screen 67, which screens out pebbles and lumps, that would otherwise go in with the sand.

The raw material, whether wet or dry, is often to considerable extent made up of hard lumps comprising grains of sand and pebbles cemented together with binder.

These lumps separate into their individual grains of sand, pebbles and binder when agitated with water and for this reason it is frequently desirable to deliver the raw material directly into the agitation compart ment before screening as indicated in Figure 2 and also in Figure 7.

In Figures 2 and 6 the centrifugal pump discharges the whole stream of mixed sand, water and binderupon the sizing screen. In practice I find it desirable to discharge the stream from the centrifugal pump back into the agitation compartment for more perfect disintegration of lumps and until proper adjustment has been made of the strength of the binder solution, and after the binder solution has been brought to proper strength it is still advantageous to return a portion of the stream'from the pump to the agitation compartment to screen out pebbles that have come in with the raw material and to secure more perfect agitation of new material added to the agitation tank.

If the larger portion of the stream be thus circulated back into the agitation compartment before going to the sizing screens most of the pebbles will be removed by the screen 84. (Figure 7) above the agitation compartment instead of going to the sizing screens.

If the whole stream be delivered to the sizing screens and the raw material is high in pebbles these pebbles unless they have already been taken out by preliminary circulation of the stream through screen 84-, disadvantageously affect the action of the sizing screens and result in inelficient screening and passage of imperfectly screened sand and pebbles over the tailing screen 85.

In some cases it may be preferable to charge the raw material upon the screen 84 in the path of the return stream from the circulating pump. lVhile this has a tendency to overload the screen 84 and be somewhat wasteful of raw material through imperfect disintegration of lumps it has the advantage that neither the pump nor the sizing screens have to handle pebbles.

I show in Figures 7 to 9 a particularly advantageous form of branching conduit adapted to turn all or any desired portion of the stream from the pump to either the sizing screens 86 or the screen 84 above the agitation compartment.

This arrangement is illustrated as comprising a branched pipe 87 having one branch 88 to the screen 84 above the agitation compartment and another branch 89 to the first sizing screen.

These branches 88 and 89 are each loosely connected so as tofreeIyturn up or down to any desired extent, the ends being adjust: ably supported, as by chains90 and 91.

If the branch 88 to the screen abovet-he agitation compartment be turned up while the other branch 89 delivering to the sizing screens is down then the whole stream will flow to. the sizing screen, and vice versa, if the'branch 89 be turned up andthe branch 88 downthe whole stream flows back into the agitation tank through the screen 841.-

By proper vertical adjustment of these two branch pipes, as at-end supporting chains 90 and 91, I find it very easy to send any desired portion of the stream from the pump in either direction.

The ca acit of the sizin screens is u D greatly affected by the presence or absence of pebbles and is much less for sand carried in a solution. rich in binder than for sand in a solution that islean in binder. hen a very rich molding sand is desired the binder.

solution must be very. rich. In this event the S1Z1Ilg screens have relatively low ca? pacity and the proportion of the stream de-, 'livered upon the s zing screens should not exceed a value that will resultin a delivery too big for the screens to handle.

In practice the sizing screens sometimes flood, binder solution and sand then passing over the tailing screen 85. with pebbles, and

I provide means for returning the tailings to the circulating stream when this happens I show for this purpose a hinged apron 92 receiving the tailings. Normally this apron slopes downward to the rear and delivers the tailings to a heap 93 at the rear of the machine, but if thetailings fiood with sand and binder solution (usually a temporary occurrence due to excessive pebbles or imperfect disintegration of lumps in the agitation compartment) the apron may be moved up so as tothrow the tailings back through the opening 94 of the apron and trough 95 leading back to the agitation tank.

Figure 7 shows this apron adjustably supported to slope outward as in the figure or inward to return the tailings' to the trough.

In Figure 2 I have shown the return from the settling compartments to the'agitation compartment to beback over thetop of par- 1 titions 30 and 29. I havefound it more advantageous to PTOVlQlQ. a separate trough 95 as seen in F gures 79. Each settling compartmentoverfiows into this trough and the. trough discharges at 96 back into the agitation compartment. g

The screens slope rearwardly and the slope is preferably adjustable, as indicated at 97 in Figures 7-9. Inthese figures opposite ends of the screens are supported by overhead links 98 and 99, screw turn-buckles at 97 providing slope adjustment.

The screens are vibrated or jigged horizontallyby eccentrics 100 and 101 upon a rapidly "revolving shaft'102. .A- rich; binder solution requires more rapid vibration of the sizing screens in order that the liquid and sand maypass through. IVith a binder solution of 1.2 a vibration of 500V. P. M.

of eccentric has been found satisfactory.

The eccentrics 100 are connected by links 103 to the sizing screens and the eccentrics 101 by links 104 to the screen 84 above the agitation compartment, so that the one shaft 102 vibrates both screens, and the shaft 102 driven by pulley 105, belt 106 and motor 107. i .The slope is made such that there is secured a proper. passage of sand progressively across the screens.

solution gradually works rearwardly, the finer sand passing through the first screen, the sand less fine passing through the second screen and so on, the tailings (pebbles) falling from the outer edge. of the last screen.

,Most of the binderjsolution passes through the first screen andfor this reason it is sometimes desirable to assist the screening action upon the latter screens by means of a stream of blnder solution which may be from the so- The stream discharged upon the first screen comprising pebbles, sand and binder compartments respectively underneath these binder or lessbinder than is desired in the finished product and the content of binder in the finished product will commercially I from binder or it may already contain more widely vary according to the particular use for which it is desired and also to a con- 1 siderable extent according to the individual views of different purchasers. 7

If the sand be already sized and the binder used is free from impurities all of the screens shown in Figures 7 to 9 may be dispensed with. r

WVhatever the character of the raw materials the initial operation produces a binder solution having a definite relation between .the-quantity'of binder and the quantity of sand present, this relation being that required to give a molding sand having the desired content of binder.

The specific gravity of the liquid in the agitation chamber will vary widely with r variation in the quantity of sand in suspension so that the specific gravity of the liquid in the agitation chamber does not initself give any indication of the strength of binder solution.

The rapidity with which sand will settle from a binder solution depends primarily upon the size and density of the grains of sand and the viscosity and density of the solution.

For practical purposes (and neglecting temperature variation which usually is not under control) the quantity of binder taken up by sand which settles through it will de pend largely upon the concentration of the binder solution, that is, upon the ratio of binder to water in the solution. If the binder solution be relatively concentrated sand will settle through it very slowly while if the binder solution is dilute sand will settle from it or in it very rapidly. The binder in the solution settles relatively very slowly. That time of settling may vary from a few minutes to many hours according to the nature of the binder and density of solution.

It is understood that by solution is here meant not true solution but what might be called a colloidal suspension or perhaps merely suspension.

The particles of binder are most minute as compared to the grains of sand so that the rate with which the sand settles through it is very great as compared to the rate with which the minute particles of binder settle.

Ihe strength of a weak binder solution containing sand may be determined easily and quickly by merely waiting a moment or so for the sand to settle and then using a hydrometer. I

If the binder solution be strong, however, the sand will not settle quickly and a long time would be required before there would be sufficient settling of the sand for the use of a hydrometer to determine the specific gravity of the binder solution (considered apart from the sand).

To quickly determine the strength of a strong binder solution containing sand, a definite volume is taken and diluted when the sand settles quickly and is measured. The solution is then further diluted to a definite volume with due correction for the amount of sand found, and this tested with a hydrometer. original binder solution is theneasily determined. from the hydrometer reading and extent of dilution.

The mixture of binder solution and sand is whipped about and circulated by the centrifugal pump until the strength of binder solution reaches the desired value.

If there be no change in the water content and the sand added already contains some hinder the concentration of the binder solution in the agitation chamber will continue to increase, whatever the amount of binder in the sand, that is, a sand very lean in binder put into a strong binder solution, that is not fully loaded with sand will increase the concentration of the binder solu- The specific gravity of the tion,-increase the ratio of binder to water present.

The operation may be continuous or intermittent. If it is continuous the sand added will usually already contain binder andthere should be maintained a definite ratio between the quantity of hinder added and the quantity of water added.

If all of the sand added already contains morebinder than is desired in the product the volume of the binder solution would gradually increase until the agitation tank overflows unless the excess binder solution be removed elsewhere.

In actual practice sufiicient sand lean in binder or perhaps containing no binder would be added to avoid this growing excess of hinder solution or else excess water would be added'to keep binder solution down to desired limits, a suitable overflow being provided.

It the sand added be all lean in binder the amount of water to be added will be in sufficient to maintain the original volume of binder solution so that additional binder should be added with a proper amount of water to maintain the proper volume of binder solution in the agitation tank.

In Figures 7 to 9 I illustrate pipes 111 from the bottom of the respective settling chambers. These pipes are provided with swiveled trough ends so as to discharge in any one of a number of pits 112.

I find in practice that a hole in the bo tom (or side near the bottom) of a settling tank, closed when not in use by an ordinary swinging closure, may serve very well for the removal of molding sand from the tank.

It is not necessary to provide specially sloping bottom to the settling compartment as in practice the sand will form its own slope provided this part of the apparatus is separated from the vibration of the machinery.

In Figure 10 the opening 113 from near the bottom of a settling compartment 114; is merely a hole normally closed by a swinging closure 115.

When the molding sand has settled within the compartment to sufficient depth the closure is opened and the hydraulic head above the opening forces the sand out into the inclined trough 116 to suitable porous receptacle 117. If bags he used the molding sand may be packed in same for shipment at the end of this trough, but must first be laid aside for drying.

I show the receptacle supported over a grating 118 above the pit 119. Normally the receptacle will be filled to slight overflowing and the overflow comprising chiefly binder solution collects in the pit.

In operation the binder content of a molding sand low in binder can be increased or percentage or hinder he reduced in a sand initially higher in binderas de sired. This can be done by strengthening orweakening the binder solution by addition of separate binder or by additionofwater respectively to control the percentage of binder in" the solution through and in which the specifications, covering by either of these methods the entire range of possible bindercontent and by screening or the use of separate screened sands and separate binders 0t dnlerent kinds covering the entire range of character of binder and percentage of binder withrespect to sand and size of grain of sand content. 7

As the process may be either continuous excess of mixed sand and binder to the screens by reason of which fine sand will be carried over the coarser screensand settle with coarser sand in the next compartment or to restrict the flow of mixed sand and binder. so that substantially all of the finer sands will be sifted out by each screen as it passes the screens, reducingor substantially eliminating the amount of finer sand settling with the coarser sand in any givencompartment. This control can be efiected readily all be settling down.

by the quantity of sand and by the solution by-passed. j I

Moreover slnce the coarser sand settles 'more quickly than the finer sand it is possible to further control the mixture of finer and coarser sands present in a compartment,

which may settle therefrom through the binder solution by intermittent operation allowing time for: coarser sand only tosettle out and then removing the solution above the settled sand in the tank. j

By settling these withdrawn solutions separately it is possible to get a molding sand of finer sand content than could be reliably separated out by screens.

ln screening sand composed of grains of several sizes through a sizing screen each section of the screen will pass all the sizes between its size ot mesh and the' next smaller mesh and, due to the more rapid settling of the grains the smaller grains will come in the next layer, but in running the process contlnuously there Wlll be no layers between grains of different size which have gone through the same screen because they will together even though at differentrates. 7 i r i v The pump and the stirring mechanism should be run continuously and at substantially the same rate during operation of the process in order that as complete a'mechanical mixture may be obtained as possible of the sand and binder whichare in suspen enough so that an excess quantity of liquid will have to be handledfor the same quantity of product passed on through the settling tanks.

For the above, reason the best resultsare ordinarily attained in the starting of the process by pumping wholly through the bypass until the binder content has reached the required degree of concentration. It may be or discontinuous it is also possible to feed an rather than to pump over intothe settling,

tanks an excessive quantity of solution for a relatively smaller percentageot sand, but

this is of less importance than is the percentage of binder in the solution.

The by-pass performs two main functions. In starting it permits the solution to be passed wholly though it until the desired binder concentration a, least and permissibly the desired sand concentration also has been attained. In operation. relative lifting of the by-pass pipe and lowering of the discharge pipe or, vice ve'r'sa, provides torvery exact adjustment of the quantity of discharge upon the screens with by-pass of any. excess pumped and without slowing the pump. At the sametime the adjustment permits discharge of the entire quantity pumped upon the screens... An excessquantity inthis case would be returned to the tank as tailings until readjustment of discharge can be made.v a i Separate binder orsand can be added initially or during the continued operation.

Vibration or the settling tank is avoided by separating the screen and shaking mechanism mechanically from the settling tank and thetime of settling and the percentage of binder content in the product are largely dependent upon the specific gravity otthe solution n thesettling tank. The sand Will separate out of a solution of 12 specific The height of the solution intlie different settling tanks is equalized Where desired by screened openings between the tanks, the screen being of such mesh as to preventfpassage of finer sand tothe tank in which the coarser sand is being settledas in Figure 7.

Of course the steps can be modified to omit functions not needed such as omitting the sizing screens where sizing of the sand is not desired or has been performed preliminarily.

The overflow from each of the tanks is returned to the mixing tank without passing across the intervening tanks in the form shown in Figures 7-9 avoiding settling of coarser sand into a tank intended for finer sand.

The permissible return of the tailings to the mixing tank provides for rehandling of any mixture which is carried over by reason of excessive feed.

Raw material is often lumpy and does not screen well until after it has been thrown into the mixing tank. The by-pass arrangement makes it possible to dump the raw material directly into the starting tank and to screen out the pebbles to advantage by a screen beneath the by-pass opening.

While the machine illustrated is adapted to prepare molding sands of widely variant required binder from widely variant raw materials, specific features advantageously vary considerably, both with the character of the raw materials and with the character of the product.

In view of my invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art and I therefore claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is 1. In a machine for mixing sand and a binder solution, a mixing chamber, a pump for removing solution from the mixing chamber, a by-pass for the material pumped adapted to return it from the pump back to the mixing chamber and a tank in addition to the mixing chamber to which tank that discharge from the pump is delivered which is not by-passed.

2. In a machine for mixing sand and a binder solution, a mixing chamber, a pump for removing solution from the mixing chamber, a bypass for the material pumped adapted to return it from the pump back to the mixing chamber and a tank in addition to the mixing chamber to which tank that discharge from the pump is delivered which is not by-passed, the quantity of material discharged and that by-passed being adjustable by control of the height of the by-pass outlet.

3. In a machine for mixing sand and binder, a mixing chamber, a pump for removing solution therefrom, a bypass for the material pumped adapted to carry the material from the pump back to the mixing chamber and a tank in addition to the mixing chamber, to which tank that dis charge from the pump is delivered which is not icy-passed, the discharge and by-pass'being adapted to turn on an outside axis so as to, control the amount of discharge by the relative heights of the discharge and byass.

p l. In a machine for mixing sand and binder, the combination of a mixing chamber, an agitator therein, a pump adapted to with draw solution from the chamber, a plurality of screens through which the pump is adapted to discharge, means for vibrating the screens, a discharge and a by-pass for controlling the quantity of discharge to the screens while the pumping rate is maintained.

5. In a machine for mixing sand and.

binder in solution, and settling them out to form a molding sand, a mixing tank, a plurality of settling tanks having overflow from each of the tanks, that from farther tanks passing the others, to the mixing tank, screens for separating the sand and pumping means for discharging the mixture upon the screens.

6. In a machine for mixing sand and binder in solution, a mixing tank, a plurality of screens, pumping means for discharging the mixture of sand and binder upon the screens, settling tanks beneath the screens and connections for overflowing each of the settling tanks to the mixing tank free from the other tanks.

7. In a machine for mixing sand and binder in solution, a mixing tank, a plurality of screens, a pump discharging the mixture upon the screens, settling tanks beneath the screens and means for flowing the tailings from the last screen controllably to a separate point or back to the mixing tank.

8. In apparatus for )reparing molding sand, an agitation cham er, a coarse screen there above, settling compartments near the agitation chamber, a sizing screen above the settling compartments, a centrifugal pump having an inlet from the agitation compartment and a delivery conduit having branches discharging respectively to the screen above the agitation compartment and to the sizing screens and means for controlling the relative flow through the branches.

9. In apparatus for preparing molding sand, an agitation chamber, a coarse screen thereabove, settling compartments near the agitation chamber, sizing screens above the settling compartments, a centrifugal pump having an inlet into the agitation compartment and a delivery conduit having branches discharging respectively to the screen above the agitation compartment and 10. In apparatus for preparing molding 5 sand an agitation chamber, settling com partments adjacent thereto, sizing screens J above the settlingcompartments, a conduit fluid return-from the settling compartments delivering intothe agitation chamber, and

a circulating pump having inlet connection into the agitation chamber and outlet connection branching to deliver one portion back into the agitation chamber and another portion to the sizing screens and'thence-to the settling compartments. c .WVAGERFISHERL 

